In recent years, in the fields of semiconductor, optical • magnetic recording, etc., as demands for higher density, higher integration and others have increased, techniques have become essential for fine pattern processing of about several hundreds to tens of nanometers or less. Therefore, to achieve the fine pattern processing, elemental techniques of each process have been studied actively such as a mask • stepper, exposure and resist material.
Many studies on the resist material are performed, and currently, the most common resist material is a photoreactive organic resist (hereinafter, also referred to as a photoresist) that reacts by an exposure light source such as ultraviolet light, electron beam and X-rays (for example, see Patent Document 1 and Non-patent Document 1).
In the laser light used in exposure, the intensity of the laser light focused by the lens generally shows the Gaussian distribution form as shown in FIG. 1. In the Gaussian distribution, the spot diameter is defined by 1/e2. In general, the reaction of a photoresist starts by absorbing energy represented by E=hν (E: energy, h: Planck constant, ν: wavelength). Accordingly, the reaction is not dependent on the intensity of the light significantly, and is rather dependent on the wavelength of the light. Thus, the reaction occurs in the entire portion irradiated with the light (portion irradiated with light≈exposed portion). Therefore, when the photoresist is used, the photoresist is faithfully exposed with respect to the spot diameter.
The method of using a photoresist is an extremely useful method in forming fine patterns of about hundreds of nanometers. However, in order to form finer patterns, it is necessary to expose with a smaller spot than a pattern required in principle. Accordingly, it is indispensable to use a KrF laser, ArF laser or the like with short wavelengths as an exposure light source. However, these light source apparatuses are remarkably large-size and expensive, and are unsuitable from the viewpoint of reducing the manufacturing cost. Further, in the case of using the exposure light source of electron beam, X-rays or the like, since it is necessary to evacuate the exposure atmosphere to a vacuum state, using a vacuum chamber is required, and there are significant limitations from the viewpoints of the cost and increases in the size.
Meanwhile, when a substance is irradiated with the laser light having the distribution as shown in FIG. 1, the temperature of the substance also shows the same Gaussian distribution as the intensity distribution of the laser light. In this case, when a resist reacting at some temperature or more i.e. heat-reactive resist is used, as shown in FIG. 2, since the reaction proceeds only in the portion becoming a predetermined temperature or more, it is made possible to expose the range smaller than the spot diameter (portion irradiated with light≠exposed portion). In other words, without shortening the wavelength of the exposure light source, it is possible to form the pattern finer than the spot diameter, and by using the heat-reactive resist, it is possible to reduce the effect of the wavelength of the exposure light source.
Reported previously were techniques for using tungsten oxide (WOx), molybdenum oxide (MoOx), noble metal oxide or the like as a heat-reactive resist, and forming a fine pattern by exposure and thermal • photoreaction with a semiconductor laser or the like (for example, see Patent Documents 2 to 4 and Non-patent Document 2). The WOx and MoOx are resist materials called the imperfect oxide such that the oxidation degree X is set at a value lower than that of the perfect oxide, and are allowed to form a fine pattern by changing the oxidation degree X by heating due to exposure, making a difference in solubility with respect to an etchant due to the difference in the oxidation degree, and etching. Therefore, etching properties are changed due to a tiny difference in the oxidation degree X, and extremely significant techniques are required in order to manufacture a resist with high reproducibility from many parameters such as a state of a starting material, method of film deposition and method of exposure. Further, there has been another problem that tungsten (W) and molybdenum (Mo) are low in resistance to dry etching using fluorocarbons.
Meanwhile, the noble metal oxide is allowed to form a fine pattern by inducing decomposition of the noble metal oxide by thermal reaction, photoreaction or the like, making a difference in solubility with respect to an etchant in the undecomposed/decomposed portions and etching. For example, in the case of thermal reaction, this method causes decomposition when the material reaches some particular temperature (decomposition temperature), is therefore not affected significantly by a state (for example, a tiny difference in the oxidation degree or the like) of the starting material, and has characteristics easy to obtain a resist with extremely good reproducibility. However, the noble metal oxide that is a decomposition material used in Patent Documents 3 and 4 causes the decomposition reaction by thermal reaction, photoreaction or the like to enable a fine pattern to be formed, but is only permitted to adopt a sea-island structure in which resist portions left after etching are random because of accompanying particle growth of the material concurrently with decomposition, and is hard to control the pattern size of a fine pattern of uniform concavo-convex, the shape of a line and the like.
Copper oxide that is a noble metal oxide causes abrupt decomposition to release oxygen when reaching the decomposition temperature, further suppresses particle growth as compared with the noble metal oxides used in Patent Documents 3 and 4, and therefore, is an effective resist material in fine pattern formation. However, as shown in Patent Documents 5 to 8, many etchants for copper exist, but there is no report on achieving selective etching of exposed portions against unexposed portions with high accuracy in performing exposure using an oxide of noble metal, particularly, an oxide of copper.